Planar nonpolar group-III nitride films grown on miscut substrates

ABSTRACT

A nonpolar III-nitride film grown on a miscut angle of a substrate, in order to suppress the surface undulations, is provided. The surface morphology of the film is improved with a miscut angle towards an a-axis direction comprising a 0.15° or greater miscut angle towards the a-axis direction and a less than 30° miscut angle towards the a-axis direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. Section 120 ofco-pending and commonly-assigned

U.S. Utility patent application Ser. No. 14/164,434, filed on Jan. 27,2014, by Asako Hirai, Zhongyuan Jia, Makoto Saito, Hisashi Yamada, KenjiIso, Steven P. DenBaars, Shuji Nakamura, and James S. Speck, entitled“PLANAR NONPOLAR GROUP III NITRIDE FILMS GROWN ON MISCUT SUBSTRATES”attorneys' docket number 30794.238-US-C2 (2007-674-4),

which application is a continuation under 35 U.S.C. Section 120 ofco-pending and commonly-assigned

U.S. Utility patent application Ser. No. 13/427,590, filed on Mar. 22,2012, by Asako Hirai, Zhongyuan Jia, Makoto Saito, Hisashi Yamada, KenjiIso, Steven P. DenBaars, Shuji Nakamura, and James S. Speck, entitled“PLANAR NONPOLAR GROUP III NITRIDE FILMS GROWN ON MISCUT SUBSTRATES”,

which application is a continuation under 35 U.S.C. Section 120 ofco-pending and commonly-assigned

U.S. Utility patent application Ser. No. 12/140,096, filed on Jun. 16,2008, by Asako Hirai, Zhongyuan Jia, Makoto Saito, Hisashi Yamada, KenjiIso, Steven P. DenBaars, Shuji Nakamura, and James S. Speck, entitled“PLANAR NONPOLAR M-PLANE GROUP III NITRIDE FILMS GROWN ON MISCUTSUBSTRATES”, now U.S. Pat. No. 8,158,497, issued Apr. 17, 2012,

which application claims the benefit under 35 U.S.C. Section 119(e) ofco-pending and commonly-assigned

U.S. Provisional Patent Application Ser. No. 60/944,206, filed on Jun.15, 2007, by Asako Hirai, Zhongyuan Jia, Makoto Saito, Hisashi Yamada,Kenji Iso, Steven P. DenBaars, Shuji Nakamura, and James S. Speck,entitled “PLANAR NONPOLAR m-PLANE GROUP III NITRIDE FILMS GROWN ONMISCUT SUBSTRATES”,

all of which applications are incorporated by reference herein.

This application is related to the following co-pending andcommonly-assigned U.S. patent applications:

U.S. Provisional Patent Application Ser. No. 60/954,770, filed on Aug.8, 2007, by Hisashi Yamada, Kenji Iso, and Shuji Nakamura, entitled“NONPOLAR III-NITRIDE LIGHT EMITTING DIODES WITH LONG WAVELENGTHEMISSION,”;

U.S. Provisional Patent Application Ser. No. 60/954,767, filed on Aug.8, 2007, by Hisashi Yamada, Kenji Iso, Makoto Saito, Asako Hirai, StevenP. DenBaars, James S. Speck, and Shuji Nakamura, entitled “III-NITRIDEFILMS GROWN ON MISCUT SUBSTRATES,”; and

U.S. Provisional Patent Application Ser. No. 60/954,744, filed on Aug.8, 2007, by Kenji Iso, Hisashi Yamada, Makoto Saito, Asako Hirai, StevenP. DenBaars, James S. Speck, and Shuji Nakamura, entitled “PLANARNONPOLAR M-PLANE GROUP III-NITRIDE FILMS GROWN ON MISCUT SUBSTRATES,”;

which applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for the growth of planarfilms of nonpolar m-plane, and more specifically, to a technique for thegrowth of an atomically smooth m-GaN film without any surfaceundulations.

2. Description of the Related Art

The usefulness of gallium nitride (GaN) and its ternary and quaternarycompounds incorporating aluminum and indium (AlGaN, InGaN, AlInGaN) hasbeen well established for fabrication of visible and ultravioletoptoelectronic devices and high-power electronic devices. Thesecompounds are referred to herein as Group III nitrides, or III-nitrides,or just nitrides, or by the nomenclature (Al, B, Ga, In)N. Devices madefrom these compounds are typically grown epitaxially using growthtechniques including molecular beam epitaxy (MBE), metalorganic chemicalvapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE).

GaN and its alloys are the most stable in the hexagonal wurtzite crystalstructure, in which the structure is described by two (or three)equivalent basal plane axes that are rotated 120° with respect to eachother (the a-axis), all of which are perpendicular to a unique c-axis.Group III and nitrogen atoms occupy alternating c-planes along thecrystal's c-axis. The symmetry elements included in the wurtzitestructure dictate that III-nitrides possess a bulk spontaneouspolarization along this c-axis, and the wurtzite structure exhibitspiezoelectric polarization.

Current nitride technology for electronic and optoelectronic devicesemploys nitride films grown along the polar c-direction. However,conventional c-plane quantum well structures in III-nitride basedoptoelectronic and electronic devices suffer from the undesirablequantum-confined Stark effect (QCSE), due to the existence of strongpiezoelectric and spontaneous polarizations. The strong built-inelectric fields along the c-direction cause spatial separation ofelectrons and holes that in turn give rise to restricted carrierrecombination efficiency, reduced oscillator strength, and red-shiftedemission.

One approach to eliminating the spontaneous and piezoelectricpolarization effects in GaN optoelectronic devices is to grow thedevices on nonpolar planes of the crystal. Such planes contain equalnumbers of Ga and N atoms and are charge-neutral. Furthermore,subsequent nonpolar layers are equivalent to one another so the bulkcrystal will not be polarized along the growth direction. Two suchfamilies of symmetry-equivalent nonpolar planes in GaN are the {11-20}family, known collectively as a-planes, and the {1-100} family, knowncollectively as m-planes.

The other cause of polarization is piezoelectric polarization. Thisoccurs when the material experiences a compressive or tensile strain, ascan occur when (Al, In, Ga, B)N layers of dissimilar composition (andtherefore different lattice constants) are grown in a nitrideheterostructure. For example, a thin AlGaN layer on a GaN template willhave in-plane tensile strain, and a thin InGaN layer on a GaN templatewill have in-plane compressive strain, both due to lattice matching tothe GaN. Therefore, for an InGaN quantum well on GaN, the piezoelectricpolarization will point in the opposite direction than that of thespontaneous polarization of the InGaN and GaN. For an AlGaN layerlatticed matched to GaN, the piezoelectric polarization will point inthe same direction as that of the spontaneous polarization of the AlGaNand GaN.

The advantage of using nonpolar planes over c-plane nitrides is that thetotal polarization will be reduced. There may even be zero polarizationfor specific alloy compositions on specific planes. Such scenarios willbe discussed in detail in future scientific papers. The important pointis that the polarization will be reduced compared to that of c-planenitride structures.

Although high performance optoelectronic devices on nonpolar m-plane GaNhave been demonstrated, it is known to be difficult to obtain smoothsurfaces for the m-plane non polar GaN. The m-plane GaN surface istypically covered with facets or rather macroscopic surface undulations.Surface undulation is mischievous, for example, because it wouldoriginate faceting in quantum structures, and inhomogeneousincorporation of alloy atoms or dopants depend on the crystal facets,etc.

The present invention describes a technique for the growth of planarfilms of nonpolar m-plane nitrides. For example, an atomically smoothm-GaN film without any surface undulations has been demonstrated usingthis invention.

SUMMARY OF THE INVENTION

The present invention discloses a method for growing planar nonpolarIII-nitride films that have atomically smooth surfaces, without anymacroscopic surface undulations, by selecting a miscut angle of asubstrate upon which the nonpolar III-nitride films are grown, in orderto suppress the surface undulations of the nonpolar III-nitride films.The miscut angle is an in-plane miscut angle towards the a-axisdirection, wherein the miscut angle is a 0.15° or greater miscut angletowards the a-axis direction and a less than 30° miscut angle towardsthe a-axis direction.

The present invention discloses a nonpolar III-nitride film growth on amiscut of a substrate, wherein a top surface of the film is a nonpolarplane and the miscut is a surface of the substrate angled at a miscutangle with respect to a crystallographic plane of the substrate.

The miscut angle may be 0.15° or greater. The crystallographic plane maybe an m-plane, the nonpolar III-nitride film may be m-plane, and themiscut angle may be towards an a-axis direction and comprise a 0.15° orgreater miscut angle towards the a-axis direction and a less than 30°miscut angle towards the a-axis direction. The top surface may beatomically smooth or planar. The miscut angle may be such that a rootmean square (RMS) step height of one or more undulations on the topsurface, over a length of 1000 micrometers, is 50 nm or less. The miscutangle may be such that a maximum step height of the undulations on thetop surface, over a length of 1000 micrometers is 61 nm or less. Theundulations may comprise faceted pyramids.

The crystallographic plane may be a nonpolar plane. The miscut angle maybe sufficiently small such that the film is nonpolar. The miscut anglemay be such that the top surface, and one or more surfaces of one ormore layers deposited on the top surface, are sufficiently smooth for aquantum well interface or a heterojunction interface.

The film may be a substrate or template and the top surface is suitablefor subsequent growth of device-quality (Al, B, Ga, In)N layers on thetop surface. A device may be fabricated using the film.

The present invention further discloses a method for growing aIII-nitride, comprising growing a nonpolar III-nitride film on a miscutof a substrate, wherein the miscut comprises a surface of the substrateangled with a miscut angle with respect to a crystallographic plane ofthe substrate, in order to increase surface flatness of the nonpolarIII-nitride film. The method may further comprise the step of selectingthe miscut angle in order to suppress surface undulations of thenonpolar III-nitride film to achieve a smooth surface morphology of thefilm. The crystallographic plane may be an m-plane, the nonpolarIII-nitride film may be m-plane, and the miscut angle may be towards ana-axis direction and comprise a 0.15° or greater miscut angle towardsthe a-axis direction and a less than 30° miscut angle towards the a-axisdirection. A nonpolar III-nitride film may be fabricated using themethod.

The present invention further discloses a nonpolar III-nitride-baseddevice comprising a nonpolar III-nitride film, having a smooth surfacemorphology, grown on a miscut of a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIGS. 1(a) and 1(b) are schematic drawings of a cross-section of a GaNfilm along the a-axis direction on a freestanding m-GaN substrate withmiscut angles.

FIGS. 2(a), 2(b) and 2(c) are optical micrographs of the surface of anm-plane GaN film grown on a freestanding m-GaN substrate with variousmiscut angles, wherein FIG. 2(a) shows the surface of an m-plane GaNfilm grown on a freestanding m-GaN substrate with a miscut angle of0.01°, FIG. 2(b) shows the surface of an m-plane GaN film grown on afreestanding m-GaN substrate with a miscut angle of 0.15°, and FIG. 2(c)the surface of an m-plane GaN film grown on a freestanding m-GaNsubstrate with a miscut angle of 0.30°.

FIG. 3 shows a root mean square (RMS) value evaluated from step heightmeasurements of an m-plane GaN pyramid feature grown on a freestandingm-GaN substrate with various miscut angle variations.

FIG. 4 shows a maximum height value evaluated from step heightmeasurements of an m-plane GaN film grown on a freestanding m-GaNsubstrate with various miscut angle variations.

FIG. 5 is a flowchart illustrating a method of the present invention.

FIG. 6 is a cross sectional schematic of a device according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

One embodiment of the present invention describes a method of obtaininga smooth surface morphology for nonpolar III-nitride films.Specifically, surface undulations of nonpolar III-nitride films aresuppressed by controlling the miscut angle of the substrate upon whichthe nonpolar III-nitride films are grown.

Current nitride devices are typically grown in the polar [0001]c-direction, which results in charge separation along the primaryconduction direction in vertical devices. The resulting polarizationfields are detrimental to the performance of current state of the artoptoelectronic devices.

Growth of these devices along a nonpolar direction has improved deviceperformance significantly by reducing built-in electric fields along theconduction direction. However, macroscopic surface undulations typicallyexist on their surfaces, which is harmful to successive film growth.

Until now, no means existed for growing nonpolar III-nitride filmswithout macroscopic surface undulations, even though they provide betterdevice layers, templates, or substrates for device growth. The novelfeature of this invention is that nonpolar III-nitride films can begrown as macroscopically and atomically planar films via a miscutsubstrate.

As evidence of this, the inventors have grown {10-10} planar films ofGaN. However, the scope of this invention is not limited solely to theseexamples; instead, the present invention is relevant to all nonpolarplanar films of nitrides, regardless of whether they are homoepitaxialor heteroepitaxial.

Technical Description

The present invention comprises a method of growing planar nonpolarIII-nitride films utilizing miscut substrates in the growth process. Forexample, it is critically important that the substrate has a miscutangle in the proper direction for growth of both macroscopically andatomically planar {10-10} GaN.

In the present invention, a GaN film was grown using a conventionalMOCVD method on a freestanding m-GaN substrate with a miscut angle alongan a-axis direction. The thickness of the GaN was 5 μm. The surfacemorphology was investigated by optical microscopy, Atomic ForceMicroscopy (AFM), and step height measurements.

FIGS. 1(a) and 1(b) are schematic drawings of the cross-section of theGaN film along the a-axis direction on an m-plane miscut substrate.Specifically, FIG. 1(a) is a schematic drawing of the cross-section ofthe GaN film 100 along the a-axis direction 102 on the surface 104 of anon-axis m-plane substrate, wherein pyramid facets 106 a, 106 b of theGaN film 100 form an isosceles triangle with an angle of a on thesubstrate 104, and FIG. 1(b) is a schematic drawing of the cross-sectionof the GaN film 108 along the a-axis direction 102 on the surface 110 ofa substrate with miscut angle of θ, wherein pyramid facets 112 a, 112 bof the GaN film 108 with angles of β and γ on the surface 110 of thesubstrate. The m-plane 114 of the substrates in FIGS. 1(a) and 1(b) isalso shown.

The inventors confirmed the same facets independent of the miscut anglesfrom AFM. Therefore, θ is defined by following equations,β=α−θ  Eq. (1)γ=α+θ  Eq. (2)θ=(β−α)/2  Eq. (3)

Experimental Results

{10-10} GaN films grown on a substrate that is nominally on-axis hasbeen found to have macroscopic surface undulations consisting offour-faceted pyramids. These pyramid facets are typically inclined tothe a, c⁺ and c⁻ directions, as shown in FIGS. 2(a) and 2(b), whereinFIG. 2(a) has a miscut angle of 0.01° and FIG. 2(b) has a miscut angleof 0.15°. It was found that a smoother surface was obtained byincreasing the miscut angle to 0.15°. It was also found that the surfaceon the substrate with a miscut angle of 0.30° has a smooth morphology,as shown in FIG. 2(c).

FIG. 3 shows the RMS values evaluated from step height measurements ofm-plane GaN pyramid features grown on substrates with various miscutangles. The RMS values over 1000 μm lengths of the films on the eachmiscut substrate were 183 nm, 121 nm, 47 nm, 7.3 nm, 13 nm, and 13 nm,for mis-orientation angles of 0.01°, 0.075°, 0.15°, 0.225°, 0.30°, and30°, respectively. The RMS values were found to decrease with increasingmiscut angles. In general, an RMS value less than 50 nm is expected foroptoelectronic and electronic devices. Thus, it is preferable that themiscut angle of the substrate be 0.15° or greater.

FIG. 4 shows the maximum step height values evaluated from step heightmeasurements of m-plane GaN pyramid features grown on substrates withvarious miscut angles. The maximum step height values over 1000 μmlengths of the films on each miscut substrate were 974 nm, 427 nm, 61nm, 14 nm, 13 nm, and 25 nm, for mis-orientation angles of 0.01°,0.075°, 0.15°, 0.225°, 0.30°, and 30°, respectively. The maximum stepheight values were found to decrease with increasing miscut angles.Judging from FIG. 4, it is preferable that the miscut angle of thesubstrate be 0.15° or greater.

Process Steps

FIG. 5 is a flowchart illustrating a method (see also FIG. 1(a) and FIG.1(b)) for growing III-nitride layers, comprising one or more of thefollowing steps:

Block 500 represents the step of selecting a miscut angle θ in order tosuppress surface undulations of the nonpolar III-nitride film.

Block 502 represents the step of obtaining a substrate having a miscutwith the desired miscut angle. The miscut may be obtained by slicing thesubstrate, or selecting a substrate with the desired miscut, forexample.

Block 504 represents the step of growing the nonpolar III-nitride layeron the miscut of the substrate, wherein the miscut comprises a surface110 of the substrate angled with the miscut angle θ with respect to acrystallographic plane 114 of the substrate, in order to increasesurface flatness of the nonpolar III-nitride film 108. Thecrystallographic plane 114 may be an m-plane, the nonpolar III-nitridefilm 108 may be m-plane, and the miscut angle θ may be towards an a-axisdirection and comprise a 0.15° or greater miscut angle towards thea-axis direction and a less than 30° miscut angle towards the a-axisdirection.

Block 506 represents a nonpolar III-nitride-based device or film grownusing the method, comprising, for example, a nonpolar III-nitride filmhaving a smooth surface morphology, grown on a miscut of a substrate,wherein the surface morphology is smoother than without the miscut.

FIG. 6 is a cross-sectional schematic of a nonpolar III-nitride film600, e.g. a growth, on a miscut 602 a of a substrate 604, wherein a topsurface 606 of the film 600 is a nonpolar plane. The miscut 602 a may bea surface 602 b of the substrate 604 angled at a miscut angle 608 withrespect to a crystallographic plane 610 of the substrate 604. Thecrystallographic plane 610 may be a nonpolar plane. The miscut angle 608may be from any crystallographic plane 610, e.g. a semipolar plane orc-plane, such that the film 600 is nonpolar or has a nonpolarorientation.

The film 600 may be an m-plane III-nitride nonpolar film such as GaN,the crystallographic plane 610 may be m-plane, and the miscut angle 608may be towards an a-axis direction 612 and comprise a 0.15° or greatermiscut angle 608 towards the a-axis direction 612 and a less than 30°miscut angle 608 towards the a-axis direction 612. However the angularrange for the miscut angle greater than 0.15° and less than 30° shouldalso hold true for other nonpolar III-nitride material films 600 (e.g.a-plane or m-plane (Al, B, Ga, In)N compounds) and with miscuts in othernonpolar directions 612 and with respect to other nonpolarcrystallographic planes 610. Therefore, the miscut angle 608 may be0.15° or greater, and less than 30°, with respect to anycrystallographic plane 610 or in any direction 612, so long as themiscut angle 608 achieves a nonpolar film 600, for example. For example,the miscut angle 608 may be sufficiently small such that the film 600 isnonpolar.

The film 600, or the top surface 606 of the film 600 may comprisesurface undulations (116 in FIG. 1(b)), which may be suppressed by themiscut angle 608 (generally, increasing the miscut angle 608 increasessuppression of the undulations 116, or increases smoothness andflatness, or reduces step height 118 a of undulations 116). The surfaceundulations 116 may comprise faceted pyramids. The miscut angle 608 maybe such that a root mean square (RMS) step height 118 a of the one ormore undulations 116 on the top surface 606, over a length of 1000micrometers, is 50 nm or less. The miscut angle 608 may be such that amaximum step height 118 a of the undulations 116 on the top surface 606,over a length of 1000 micrometers is 61 nm or less. The surfaceundulations 116 may be suppressed by the miscut angle 608 such that astep height 118 a of the undulations 116 is less than the step height118 b of undulation(s) 120 without the miscut. The film 600 may comprisea top surface 606 which is atomically smooth, planar, flat, or facetted.

Surface undulations 200 a and 200 b are also shown in FIGS. 2(a) and2(b), respectively. In FIG. 2(b), the miscut angle θ is increased sothat the surface undulations 200 b are suppressed as compared to surfaceundulations 200 a. In FIG. 2(c), the miscut angle θ is increased stillfurther so that the surface undulations are suppressed even further orare non-existent.

The film 600 may further comprise III-nitride 614 a deposited on the topsurface 606. The miscut angle 608 may be such that the top surface 606,and/or surface(s) 614 b of one or more layers 614 a grown on the topsurface 600, are sufficiently smooth for a quantum well interface (e.g.between a quantum well layer and a barrier layer) or a heterojunction.The film 600 may be a substrate or template, and the top surface 606 maybe sufficiently smooth for subsequent growth of device quality (Al, B,Ga, In)N compound layers 614 a (e.g. optoelectronic or transistor devicelayers) on top surface 606.

The film 600 is typically a direct growth rather than a lateralepitaxial overgrowth. The film 600 may be one or more layers having anythickness, i.e. a thick or thin layer. The film 600 may be thick enoughto be a bulk crystal or free standing substrate for example.

A device 616, such as laser, light emitting diode, or transistor, may befabricated using the film 600. For example, the film 600 may comprisedevice layers. Or device layers 614 a may be deposited on the surface ofthe film 600. The device layers 600, 614 a might be p-n junction layers,active layers, quantum well layers, barrier layers, or heterojunctionlayers, for example. The growth 600 may be removed from the substrate604 to provide a free standing growth or film.

Possible Modifications and Variations

In addition to the miscut GaN freestanding substrates described above,foreign substrates, such as m-plane SiC, ZnO, and γ-LiAlO2, can be usedas a starting material as well.

Although the present invention has been demonstrated using GaN films,AlN, InN or any related alloy can be used as well.

The present invention is not limited to the MOCVD epitaxial growthmethod described above, but may also use other crystal growth methods,such as HVPE, MBE, etc.

In addition, one skilled in this art would recognize that thesetechniques, processes, materials, etc., would also apply to miscutangles in other directions, such as the c-axis direction, with similarresults.

Advantages and Improvements

On-axis m-plane GaN epitaxial layers always have pyramid shaped featureson their surfaces. By controlling the crystal miscut direction andangle, smooth surfaces can be obtained, and thus high quality devicestructures can achieved.

For example, a laser diode with smooth quantum well interfaces wouldenhance the device's performance. In another example, a smooth interfacefor heterostructure epi devices, such as high electron mobilitytransistors (HEMTs) or heterojunction bipolar transistors (HBTs), wouldreduce carrier scattering and allow higher mobility of two dimensionalelectron gas (2 DEG). Overall, this invention would enhance theperformance of any device where active layer flatness is crucial to thedevice performance.

In addition, the enhanced step-flow growth mode via a miscut substratecould suppress defect formation and propagation typically observed inGaN films with a high dopant concentration. Moreover, this would enlargethe growth window of m-GaN, which would result in a better yield duringmanufacture and would also be useful for any kind of lateral epitaxialovergrowth, selective area growth, and nano structure growths.

CONCLUSION

This concludes the description of the preferred embodiment of thepresent invention. The foregoing description of one or more embodimentsof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A method for growing a nonpolar III-nitride film,comprising: selecting a miscut angle to suppress surface undulations ofthe nonpolar III-nitride film; obtaining a substrate having a miscutwith the miscut angle; and growing the nonpolar III-nitride film on themiscut of the substrate.
 2. The method of claim 1, wherein the nonpolarIII-nitride film grown on the miscut of the substrate has a surfacemorphology that is smoother than a surface morphology of a nonpolarIII-nitride film grown on a substrate without the miscut.
 3. The methodof claim 2, wherein the surface morphology has no macroscopic surfaceundulations.
 4. The method of claim 1, wherein the substrate having themiscut is obtained by slicing the substrate.
 5. The method of claim 1,wherein the miscut comprises a surface of the substrate angled with themiscut angle with respect to a crystallographic plane of the substrate.6. The method of claim 5, wherein the crystallographic plane is anm-plane, the nonpolar III-nitride film is an m-plane, and the miscutangle is towards an a-axis direction.
 7. The method of claim 6, whereinthe miscut angle comprise a 0.15° or greater miscut angle towards thea-axis direction and a less than 30° miscut angle towards the a-axisdirection.
 8. The method of claim 1, wherein the miscut angle is suchthat a root mean square (RMS) step height of the surface undulations,over a length of about 1000 micrometers, is about 50 nm or less.
 9. Themethod of claim 1, wherein a top surface of the nonpolar III-nitridefilm is a nonpolar plane.
 10. The method of claim 1, wherein thenonpolar III-nitride film is sufficiently smooth for subsequent growthof device quality (Al, B, Ga, In)N compound layers.
 11. Anoptoelectronic device, comprising: a nonpolar III-nitride film grown ona miscut of a substrate; wherein a miscut angle is selected to suppresssurface undulations of the nonpolar III-nitride film and the miscut ofthe substrate has the miscut angle.
 12. The device of claim 11, whereinthe nonpolar III-nitride film grown on the miscut of the substrate has asurface morphology that is smoother than a surface morphology of anonpolar III-nitride film grown on a substrate without the miscut. 13.The device of claim 12, wherein the surface morphology has nomacroscopic surface undulations.
 14. The device of claim 11, wherein thesubstrate having the miscut is obtained by slicing the substrate. 15.The device of claim 11, wherein the miscut comprises a surface of thesubstrate angled with the miscut angle with respect to acrystallographic plane of the substrate.
 16. The device of claim 15,wherein the crystallographic plane is an m-plane the nonpolarIII-nitride film is an m-plane, and the miscut angle is towards ana-axis direction.
 17. The device of claim 16, wherein the miscut anglecomprise a 0.15° or greater miscut angle towards the a-axis directionand a less than 30° miscut angle towards the a-axis direction.
 18. Thedevice of claim 11, wherein the miscut angle is such that a root meansquare (RMS) step height of the surface undulations, over a length ofabout 1000 micrometers, is about 50 nm or less.
 19. The device of claim11, wherein a top surface of the nonpolar III-nitride film is a nonpolarplane.
 20. The device of claim 11, wherein the nonpolar III-nitride filmis sufficiently smooth for subsequent growth of device quality (Al, B,Ga, In)N compound layers.